Fillers and pigments are key components in many industrial markets, such as paper, paints, plastics, concrete, and pharmaceuticals. Filler and pigments are utilized to reduce cost, improve functionality, and to improve the end use performance. One widely used pigment is titanium dioxide (TiO2), which is used to provide brightness and light scattering properties. Another widely used pigment is fumed silica, which may be added to some compositions to provide thixotropic attributes, for example, in paint products. A different product, but with a similar sounding name, is silica fume, which will also be further discussed below.
In paper products, commodity filler or pigment products such as synthetic precipitated calcium carbonate (PCC), or ground calcium carbonate (GCC) are often used. Various forms of PCC used include calcite crystalline structures, aragonite crystalline structures, and rhombohedral crystalline structures. Such crystalline structures are generally characterized by low aspect ratios, moderate brightness, and moderate light scattering power. Some of such materials provide improved optical properties. And, some of such materials provide desired attributes such as paper strength, when used in paper furnish, or in paper coatings. However, there remains a significant need in various paper products for fillers and/or pigments which might improve light scattering power. Similarly, in certain paint products, and uses thereof, there remains a need for improved light scattering power in fillers and/or pigments.
Titanium dioxide is one of the most widely used pigments in many industries, such as paints, paper, coatings, and in some composites. Such use may often be to improve brightness, and to improve opacity. The latter property, improved opacity, improves the light scattering properties, which makes a product have lowered see-through properties. For example, thin papers may be made more opaque (as if actually thicker) by the use of fillers with opacifying properties. The provision of such properties in products using titanium dioxide is primarily due to a combination of characteristics of titanium dioxide, such as a high refractive index (in the range of from about 2.49 to about 2.61), a small particle size (often in the 0.2 to 0.4 micron size), and in the manner in which adjacent particles of titanium dioxide pack when used. However, despite having a unique shape, size, and crystal structure, titanium dioxide has certain limitations. First, it has a very high density (about 4.2 grams per cubic centimeter). Further, in order to keep small titanium dioxide particles from agglomerating in various compositions, dispersants may be used. Such dispersants usually have deleterious effects on the strength properties, especially in coated paper. Also, titanium dioxide particles are highly abrasive. Finally, due to the complexity of some widely used manufacturing processes, which may include certain complex separation and purification processes, titanium dioxide is one of the most expensive fillers and/or coating pigments currently available.
Another filler and/or pigment found in various applications is fumed silica. Fumed silica (also called pyrogenic silica) is generally manufactured from flame pyrolysis of silicon tetrachloride, or by the vaporization of quartz in a 3,000° C. arc furnace. The primary particle surface area of most fumed silica is in the range of from about 50 to about 600 square meters per gram. And, amorphous fumed silica particles may be fused into chainlike secondary particles which, in turn, agglomerate into tertiary 3-dimensional particles. On limitation is of such material is that it is non-porous. Also, fumed silica is generally highly thixotropic, and may cause high viscosity compositions when added to paints and coatings. Also, the environmental impacts of the manufacturing process, and the usually high cost of fumed silica, limit its use.
Silica fume (also called micro-silica, and not to be confused with fumed silica) is an amorphous (i.e., non-crystalline) material. Silica fume is often collected as an ultra-fine powder as a by-product of silicon or ferro-silicon alloy production. Silica fume is generally in the form of spherical particles with an average particle size of about 150 nanometers, and with a surface area in the range of from about 15 to about 30 square meters per gram. Also, silica fume is a highly pozzolinic material, and thus may be used in cement and concrete to enhance compressive strength, bond strength, and abrasion resistance. However, at this time, silica fume, being a byproduct of production of other materials, is in relatively short supply.
The just discussed fillers and/or pigments are generally of limited purpose, as each may have a single or limited number of product enhancing properties. Thus, there remains an as yet unmet need for a multi-functional filler and/or pigment product that may, in many applications, replace expensive fillers such as titanium dioxide, fumed silica, or silica fume. It would be advantageous if such a new filler and/or pigment provided a combination of at least some ideal properties, such as high surface ratio, a high aspect ratio, a high brightness, and a high light scattering coefficient. And it would be even more advantageous if such a multi-functional filler and/or pigment were environmentally safe, and available at prices competitive with expensive fillers such as titanium dioxide, fumed silica, or silica fume. Consequently, provision of a unique multi-functional filler and/or pigment is believed to be an interesting and significant contribution to the art and science of fillers and pigments.
In the various figures of the drawing, like features may be illustrated with the same reference numerals, without further mention thereof. Further, the foregoing figures are merely exemplary, and may contain various elements that might be present or omitted from actual implementations of various embodiments depending upon the circumstances. An attempt has been made to provide the figures in a way that illustrates at least those elements that are significant for an understanding of the various embodiments and aspects of the developments described herein. However, various other elements for a multi-functional filler and/or pigment, especially as applied for various compositions using the same, may be utilized in order to provide useful, reliable, and highly functional fillers and/or pigments.